Two speed accessory transmission with optional neutral mode

ABSTRACT

An accessory transmission for an automotive vehicle comprises a planetary gear set, a fixed cover and a cone clutch engageable with the ring gear of the planetary gear set or the cover to provide a direct drive or underdrive gear ratio in one embodiment, or a direct drive and overdrive gear ratio in another embodiment. The principles of the invention may also be applied to an embodiment wherein the ring gear rotation is governed by a one way clutch as well as the cone clutch to provide both underdrive and overdrive transmissions.

This invention relates to an accessory drive or transmission associatedwith an engine. In particular, the invention provides a two speedaccessory drive which may include a neutral gear ratio for drivingengine accessories which in an automotive vehicle may include thealternator, water pump, power steering pump and air conditionercompressor. The invention may be adapted to provide an underdrive oroverdrive gear ratio, which in either case provides a reduction ratiofor the accessories at a selected increasing engine speed. The inventionmay provide any gear ratio which can be obtained using a planetary gearsystem. Typically, the invention is substituted for the enginecrankshaft pulley of a vehicle, but may be made small enough to besubstituted for a drive pulley of an accessory.

With the recent emphasis on energy conservation and fuel economy forautomobiles, the need for the development of a suitable transmission fordriving the accessories has presented itself. Running the accessoriesdirectly off of the crankshaft of the engine is inefficient at moderateto high engine speeds and in fact may cause damage to or reduce the lifeof the accessories. Thus, accessories driven directly by the engine mustbe made to withstand the abuse of high speed driving. Directly drivingthe accessories also results in a significant horsepower drain on theengine. A considerable amount of the available horsepower of the enginemay be used to drive the accessories in a direct drive arrangement.

By providing an accessory transmission which enables the accessories tobe driven at a reduced gear ratio at higher engine speeds relative tothe drive mode at lower engine speeds, the available engine horsepowercan be more efficiently employed. More of the available horsepower maybe used for operation of the vehicle, thus improving vehicleperformance. The efficiency provided by the invention will also resultin fuel savings. Also, since at higher engine speeds the accessories aredriven at relatively lower speeds compared to a direct drivearrangement, there will be less wearing forces applied thereto whichshould result in longer life for the accessories.

Problems facing car makers when developing an accessory transmissioninclude the need to develop a device which is lightweight, simple,inexpensive and fully enclosed. It is quite desirable to have anaccessory drive which was fully enclosed to the outside environment sothat the drive mechanism is isolated from the adverse effects of rain,dust, corrosive agents and the like.

Another problem facing the designer of an accessory drive for an engineis the need to overcome the torsional effects transmitted to the gearsystem thereof from the engine input. The torsional effect is caused bythe firing sequence of the engine and is higher in engines having alower number of cylinders because each piston in the engine is requiredto contribute proportionally more to the rotation of the drive shaftwhen at a greater piston angle. For example, the piston angle in a fourcylinder engine is 90°, whereas in an eight cylinder engine it is 45°.Because of the increased torsional effect associated with a fourcylinder engine, the accessory drive will be noisy and the gear systemwill be subject to premature failure unless means for damping thetorsional effect is provided.

Accordingly, the invention provides a sun gear held underdrive accessorytransmission associated with an engine comprising, a planetary gear setcomprising a sun gear having an integrally formed shaft, a plurality ofplanet gears positioned about and drivingly engaging the sun gear, aplanet gear carrier, and a ring gear positioned about and drivinglyengaging the planet gears, wherein said ring gear provides rotationalinput to the transmission from the vehicle engine. A fixed cover isprovided for the transmission, and a cone clutch is slidably affixed onthe shaft of the sun gear and has frustoconical working surfacesengageable with compatible surfaces of either the ring gear or thecover. Means are provided for sliding the cone clutch axially along theshaft of the sun gear. An output shaft is affixed to the planet gearcarrier, and the sun gear is supported by a bearing about the outputshaft. Preferably, especially in association with an engine in which thetorsional effect causes excessive noise or rattling, a one way clutchwith support bearings is positioned between the sun gear or ring gearand the output shaft which allows the output shaft to rotate only in thedirection of engine rotation.

The invention also provides a sun gear held overdrive accessorytransmission associated with an engine, comprising, a planetary gear setcomprising a sun gear having an integrally formed shaft, a plurality ofplanet gears positioned about and drivingly engaging the sun gear, aplanet gear carrier, and a ring gear positioned about and drivinglyengaging the planet gears, wherein said ring gear provides rotationaloutput from the transmission. A fixed cover is provided for thetransmission, and a cone clutch is slidably affixed on the shaft of thesun gear and has frustoconical working surfaces engageable withcompatible surfaces of either the ring gear or the cover. An input shaftfor providing rotational input to the transmission from the vehicleengine is affixed to the planet gear carrier, and the ring gear issupported by a bearing about the input shaft. Preferably, especially inassociation with an engine in which the torsional effect causesexcessive noise or rattling, a one way clutch with support bearings ispositioned between the ring gear and the input shaft which allows thering gear to rotate only in the direction of engine rotation. Inaddition, the one way clutch carries the torque when the output speedequals the input speed.

Employing the principles of the invention, a ring gear held underdriveaccessory transmission associated with an engine is provided, comprisinga planetary gear set comprising a sun gear, a plurality of planet gearspositioned about and drivingly engaging the sun gear, a planet gearcarrier having an integrally formed shaft for providing rotationaloutput from the transmission, and a ring gear positioned about anddrivingly engaging the planet gears. An input shaft provides rotationalinput to the transmission from the engine, said sun gear being affixedabout the input shaft, and said gear carrier being supported about theinput shaft by a bearing. A cone clutch is slidably affixed on the shaftof the planet gear carrier and is capable of movement axially along theshaft, the clutch having a frustoconical working surface engageable witha compatible surface of the ring gear. Means are provided for slidingthe cone clutch axially along the shaft of the gear carrier, and a fixedcover for the transmission is supported about the shaft of the gearcarrier by a bearing, and about the ring gear by a one way clutch andbearings, said one way clutch allowing the ring gear to rotate only inthe direction of engine rotation.

Similarly the invention provides a ring gear held overdrive accessorytransmission associated with an engine, comprising a planetary gear setcomprising a sun gear, a plurality of planet gears positioned about anddrivingly engaging the sun gear, a planet gear carrier having anintegrally formed shaft for providing rotational input from the engine,and a ring gear positioned about and drivingly engaging the planetgears. An output shaft provides rotational output from the transmission,said sun gear being affixed about the output shaft, and said gearcarrier being supported about the output shaft by a bearing. A coneclutch is slidably affixed on the shaft of the planet gear carrier andis capable of movement axially along the shaft, the clutch having afrustoconical working surface engageable with a compatible surface ofthe ring gear. Means are provided for sliding the cone clutch axiallyalong the shaft of the gear carrier, and a fixed cover for thetransmission is supported about the shaft of the gear carrier by abearing, and about the ring gear by a one way clutch and bearings, saidone way clutch allowing the ring gear to rotate only in the direction ofengine rotation.

Preferred embodiments of the invention will be described with referenceto the drawings in which:

FIG. 1 is a quarter sectional view of a sun gear held underdrivetransmission in accordance with the invention;

FIG. 2 is a quarter sectional view of a sun gear held overdrivetransmission in accordance with the invention;

FIG. 3 is a quarter sectional view of a ring gear held underdrivetransmission in accordance with the invention;

FIG. 4 is a quarter sectional view of a ring gear held overdrivetransmission in accordance with the invention; and

FIGS. 5 and 6 are graphs showing horsepower savings using the invention.

Referring to FIG. 1, a preferred underdrive transmission is illustratedcomprising a planetary gear set having a sun gear 11 with a shaft 12 anda sun wheel 13. A plurality of planet gears 15 are positioned about thesun gear 11 and are in driving engagement therewith. Each planet gear 15is rotatably supported about a needle bearing 17 on a shaft 18 which iscarried by a planet carrier 20. Thrust washers 21 are provided on eitherside of each planet gear 15 to keep each planet gear 15 in axialposition on the shaft 18. A ring gear 23 is positioned about and is indriving engagement with the planet gears 15. The ring gear 23 has anintegrally formed shaft 24 which is directly connected to the crankshaftor drive of the engine through an input member 25. Rotation of the ringgear 23 is supported by ball bearings 27 and 28. The bearing 28 isoptional.

The planet gear carrier 20 is firmly attached to an output shaft 35 bymeans of a central cylindrical portion 37 formed integrally with theplanet carrier 20. Thus, rotation of the planet carrier 20 providesrotation to the output shaft 35. Rotation of the shaft 35 is supportedby ball bearings 28, 38 and 39.

Preferably, the sun gear 11 is supported axially and radially about theoutput shaft 35 by ball bearings 39 which preferably form a part of aone way clutch assembly 40. The one way clutch 40 is of a type wellknown in this art, and the clutch 40 is provided with internal rollerswhich carry the torque from the shaft 35. The clutch 40 allows theoutput shaft 35 to rotate only in the direction of engine rotation andprevents counterrotation. The one way clutch 40, therefore, provides adamping of the torsional effect from the engine thereby addressing oneof the aforementioned problems. Where the torsional effect is not aproblem, the clutch 40 may be eliminated. Of course, a single or doublebearing 39 would in any case be required to take the axial and radialload about the shaft 35. It should also be apparent to the skilledperson that the one way clutch 40 and bearings 28 may be positionedbetween the shaft 35 and the ring gear 23 (FIG. 7).

A cone clutch 46 is slidably attached to the shaft 12 of the sun gear11. This attachment is preferably accomplished by providing splineslongitudinally in the shaft along which teeth 47 about the hub of theclutch 46 may slide. The cone clutch 46 has frustoconical workingsurfaces 49 and 50. The inner surface 49 may engage a compatibly shapedouter surface 55 of the ring gear 23 by causing the cone clutch 46 toslide along the shaft 12 toward the ring gear 23.

A first cover portion 59 is provided about the transmission, and issealingly joined to a second cover portion 60 which is fixed in placepreferably by bolting it to the engine block. The cover 59 has an innersurface 62 which is compatibly shaped with the outer frustoconicalsurface 50 of the cone clutch 46. The outer surface 50 may engage theinner surface 62 of the cover 59 by causing the clutch 46 to slide alongthe shaft 12 of the sun gear 11 away from the ring gear 23.

Movement of the cone clutch 46 along the shaft 12 of the sun gear 11 maybe accomplished in a number of ways. A preferred means for activatingthe cone clutch 46 is shown in FIG. 1. A spring 65 is provided between astepped portion 66 of the sun gear shaft 12 and the cone clutch 46 whichprovides the force for pushing the clutch 46 into engagement with thecover 59. In opposition to the spring 65 is preferably a hydraulicallyactivated annular thrust bearing 69. The bearing 69 is operated by anannular hydraulic actuator 70 and causes the cone clutch 46 to movealong the shaft 12 into engagement with the ring gear 23. It will beapparent to those skilled in this art that actuation of the cone clutch46 may be accomplished, for example, by an actuator 70 having a built inrotating element (not shown) for moving the cone clutch 46 axially alongthe shaft 12. Of course, electromechanical actuator means or other knownmeans may be used to activate the cone clutch 46. In application wherethe neutral gear ratio of the transmission is important, anelectromechanical actuator 70 would likely be preferred.

The underdrive transmission shown in FIG. 1 has three modes of operationall of which are governed by the location of the cone clutch 46 relativeto the cover 59 and the ring gear 23. For the purpose of drivingaccessories such as the alternator, water pump, power steering pump andair conditioner compressor, the output shaft 35 is attached to a pulley73 capable of receiving the required number of belts to run the variousaccessories.

At low engine revolutions (see FIG. 5), the accessory transmission mayprovide a direct drive from the engine to the output shaft 35 and pulley73 by causing the cone clutch 46 to engage the ring gear 23. This isaccomplished by triggering the hydraulic actuator 70 to extend thethrust bearing 69 which pushes the cone clutch 46 along the shaft 12 ofthe sun gear 11 so that the clutch 46 engages the ring gear 23 at thefrictional engagement of the opposing surfaces 49 and 55. Thisarrangement of components tends to cause the planetary gear set,comprising the sun gear 11, planet gears 15, planet carrier 20 and ringgear 23 to rotate as a unit to directly transmit the rotational inputfrom the ring gear 23 to the planet carrier 20 and hence, to the outputshaft 35 and the pulley 73.

A second mode of operation is provided for higher engine revolutions andis an underdrive or reduced gear ratio (see FIG. 5). The purpose ofproviding a reduced gear ratio for the transmission output is therecognition that at higher engine revolutions, the accessories do notrequire proportionally as much power to operate as is the case at lowerrevolutions. Also, the drain on engine power by the accessories is inexcess of their actual power requirements at higher engine revolutionsand is thus, not fuel efficient.

The actual engine speed at which the underdrive mode of operation isinitiated depends on a number of variables specific to the particularapplication as will be appreciated by those skilled in this art.Generally in association with an automobile, the underdrive mode will beactivated in the 800 to 1600 rpm range for the engine. This mode ofoperation is accomplished by causing the activator 70 to release thethrust bearing 69 and allow the cone clutch 46 to disengage the ringgear 23 under the influence of the force from the spring 65. The spring65 causes the cone clutch 46 to engage the stationary cover 59 so thatthe surface 50 of the clutch 46 and the surface 62 of the cover 59 comeinto a firm frictional engagement. This arrangement of components causesthe sun gear 11 to cease rotation and the input through the ring gear 23is then subjected to the gear reduction provided by the planet gears 15which is in turn transmitted to the output shaft 35 through the planetgear carrier 20.

As will be apparent to those skilled in this art, the invention providesany gear ratio which may be achieved by a planetary gear set. Therefore,the present transmission is suitable for a wide variety of applicationsand may be adapted for use in association with virtually any knownautomotive engine and combination of accessories. Also, it should beclear that the invention is not intended to be limited to automotiveapplications.

A neutral mode of operation wherein rotational energy from the engine isnot transmitted to the output shaft 35 is provided when the cone clutch46 is positioned between the ring gear 23 and the cover 59. The neutralmode of operation requires regulation of the axial movement of the coneclutch 46 by the actuator 70. This regulation may be more easilyaccomplished by an electromechanical actuator 70. The neutral mode isprovided for use in association with an accessory which is notconstantly used, such as an air conditioner.

Smooth operation of the transmission is provided by the operation of theactuator 70 and the friction surfaces 49 and 50 of the cone clutch 46.Well known means (not shown) are used to monitor the rotational speed ofthe engine and to cause hydraulic fluid to be pumped into or out of theactuator 70 through a line 76 for a smooth operation of the cone clutch46. Likewise, the torsional vibration provided to the input of thetransmission from the firing sequence of the engine cylinders iseliminated by the one way clutch 40 located between the sun gear 11 andoutput shaft 35. This is a particularly preferred addition to thetransmission in association with four cylinder engines in which thetorsional effect is especially pronounced. Suitable one way clutches forthis type of application are well known in the art and may comprise acylindrical housing having an internal needle bearing wherein theindividual rollers are mechanically disposed to rotate in one directiononly. The one way clutch 40 prevents counterrotation of the output shaft35, thereby damping the input torsional effect. In addition to reducingthe noise or rattle of the transmission caused by the torsional effect,the one way clutch 40 serves to protect the planetary gear set frompremature wear and damage to the gear teeth which otherwise would resultfrom a marked torsional effect.

Having an understanding from the foregoing description of theconstruction and operation of the underdrive transmission of theinvention, FIG. 2 illustrates the invention as applied to an overdriveaccessory transmission. As with the underdrive transmission, thetransmission shown in FIG. 2 has a planetary gear set comprising a sungear 111 having a shaft 112 and a sun wheel 113, a plurality of planetgears 115, a planet gear carrier 120 and a ring gear 123. In this case,however, the planet gear carrier 120 is attached by means of acylindrical portion 125 to an input shaft 127. The input shaft 127 isconnected directly to the engine through an input member 129.

The output of the transmission shown in FIG. 2 is through the ring gear123 to a pulley 131 affixed thereto. Preferably, a one way clutch 135and support bearings 136 are provided between the ring gear 123 and theinput shaft 127, the clutch 135 carrying the torque from the engine andproviding damping of the aforementioned torsional effect, and thebearings 136 providing axial and radial support about the shaft 127. Aswith the underdrive transmission, a cone clutch 137 is splined onto thesun gear shaft 112. A first cover portion 140 is provided about thetransmission, and the cover 140 is sealingly affixed to a second coverportion 141. The first portion 140 is supported about the ring gear 123by a bearing 161, and the second portion 141 is supported about theshaft 127 by a bearing 162. The cover members 140 and 141 are fixed inplace by bolting to the engine block.

The cone clutch 137 has frustoconical friction or working surfaces 143and 144 which are engageable with a compatible surface 147 of the ringgear 123 or 148 of the cover 140. The cone clutch 140 may be slidlongitudinally along the shaft 112 of the sun gear 111 by means of aspring 151 or a thrust bearing 153 opposing the spring 151 and operatedby an actuator 154.

In contrast to the underdrive embodiment, the transmission shown in FIG.2 has only two modes of operation, namely overdrive and direct drivemodes. In the overdrive mode, the output rotation at the pulley 131 isgreater than that of the input at the shaft 127. In the direct drivemode, the input and output rotational speeds are equal. A neutral modemay be obtained by elimination of the one way clutch 135.

The high gear or overdrive mode of operation occurs when the cone clutch137 is engaged with the cover 140 so that the opposing surfaces 144 and148 make firm frictional contact. This causes the sun gear 111 to be thestationary member of the planetary gear set so that a stepped up gearratio is provided to the ring gear 123.

The direct drive mode is provided by causing the actuator 154 to extendthe thrust bearing 153 against the cone clutch 137 thereby sliding italong the sun gear shaft 112 against the force of the spring 151 todisengage the clutch 137 from the cover 140. The preferred embodiment ofthe invention includes the one way clutch 135 for carrying the torquefrom the input shaft 127. In the overdrive transmission shown in FIG. 2,the disengagement of the cone clutch 137 from the cover 140 causes thering gear 123 to begin losing rotational speed under the load of theaccessories. As the ring gear 123 slows down to the speed of the inputshaft 127, the one way clutch 135 locks these input and output memberstogether to provide a direct drive mode of operation. The engagement ofthe cone clutch 137 with the ring gear 123 provides additional supportto the rotation of the planetary gear set as a unit. Clearly, the use ofthe one way clutch 135 enables the cone clutch 137 to provide asecondary function when engaging the ring gear 123, that is, the coneclutch 137 holds the sun gear 111 and the ring gear 123 together,thereby preventing vibration and allowing smooth rotation of the gearset as a unit. Without the inclusion of the one way clutch 135, the coneclutch 137 must be moved into firm engagement with the ring gear 123 atthe opposing surfaces 143 and 147.

As can be seen from the foregoing, the geared down mode of operation inthe overdrive transmission is provided in the direct drive mode. Thus,at lower engine revolutions, the overdrive transmission is in theoverdrive mode (see FIG. 6) which by adjustment of the pulley sizesapproximates the power transmission to the accessories obtainable at lowengine speeds without use of the invention. At the switching speed whenthe engine is in the overdrive mode, the actuator 154 causes the coneclutch 137 to disengage the cover 140 to give a direct driveconfiguration which, in effect, is a gear reduced mode.

As seen in FIG. 2, the one way clutch 135 is positioned between theinput shaft 127 and the ring gear 123. The clutch 135 allows the ringgear 123 to rotate faster than the shaft 127, but locks the ring gear123 when its speed is reduced to that of the shaft 127. Clearly, the oneway clutch 135 also prevents any tendency for the ring gear 123 tocounterrotate due to the engine torsional effect.

The principles of the invention may also be expressed by governing therotation of the ring gear by means of a one way clutch rather than thecone clutch. In these embodiments shown in FIGS. 3 and 4, the gearreduction or enhancement is achieved by holding the ring gear stationaryrather than in the previously discussed embodiments wherein the sun gearwas held stationary.

The embodiment of the invention shown in FIG. 3 is an underdriveaccessory transmission having an input shaft 212 connected to the enginedrive by means of a flanged attachment means 214. A planetary gear setis provided comprising, a sun gear 222 affixed to and driven by theshaft 212, a plurality of planet gears 224 positioned about and indriving engagement with the sun gear 222, and a ring gear 226 positionedabout and in driving engagement with the planet gears 224.

The planet gears 224 are supported by a planet gear carrier 232 having apin 236 and needle bearing 238 for each planet gear 224. Thrust washers239 are provided about each planet gear 224 to inhibit axial movement ofthe gears 224 on the pins 236. The planet carrier 232 is supported by acylindrical portion 246 formed integrally therewith about a one wayclutch 248 and bearings 249 provided about the shaft 212. The preferablyintegrally formed bearing portions 249 of the clutch 248 provides axialand radial support for the planet gear carrier 232 about the shaft 212.The one way clutch 248 only allows rotation of the shaft 212 in thedirection of engine rotation. This clutch 248 performs the same functionas the clutch 40 shown in FIG. 1, i.e., it damps the torsional effectsof the engine, and as with the clutch 40, the clutch 248 may also bepositioned between the shaft 212 and the ring gear 226.

The cylindrical portion 246 of the carrier 232 is splined to allowmovement of a cone clutch 250 axially along it under the opposinginfluences of a spring 252 and a thrust bearing 255. The thrust bearing255 is controlled preferably by an annular hydraulic actuator 257.

The ring gear 226 is supported about the input shaft 212 by a bearing263 which allows the shaft 212 to rotate relative the ring gear 226. Afirst cover member 265 is supported relative to the ring gear 226 by aone way clutch 270 and support bearings 271. The clutch 270 allows thering gear 226 to rotate in the direction of engine rotation only, andthe bearings 271 provide axial and radial support for the ring gear 226about the cover member 265.

In this embodiment, the output is the planet gear carrier 232, and apulley 275 is affixed to the cylindrical portion 246 of the carrier 232.A second cover member 277 is sealingly joined to the first cover member265 such as by bolts 278 and an O-ring 279, and is supported about theoutput cylindrical portion 246 by a bearing 280.

This ring gear held underdrive unit has a direct drive mode of operationwherein the output pulley 275 rotates at the speed of the input shaft212, and a gear reduced mode of operation wherein the pulley 275 rotatesat a speed less than that of the input shaft 212.

The direct drive mode is provided when the cone clutch 250 engages thering gear 226 by causing the thrust bearing 255 to slide the clutch 250axially along the cylindrical portion 246 of the planet gear carrier232. In this regard, the cone clutch 250 is provided with a frictionalworking surface 283 which is engageable with a compatible outer surface284 of the ring gear 226. Engagement of the cone clutch 250 and the ringgear 226 causes the locking together of the ring gear 226 and planetgear carrier 232 thereby causing the planet gear system to rotate as aunit.

At the desired switching speed, during engine acceleration, the actuator257 releases the thrust bearing 255 allowing the cone clutch 250 todisengage the ring gear 226 under the influence of the spring 252. Thering gear 226 is prevented from counterrotation by means of the one wayclutch 270 and is, therefore, held stationary. The planet gear system isthen able to provide a gear reduction from the sun gear 222 input to theplanet gear carrier 232 output. The one way clutch 248 preventscounterrotation of the input shaft 212 thereby damping the torsionaleffect.

It will be noted that because the various members comprising a planetarygear set are obviously interrelated, i.e., the ring gear, sun gear andplanet gear carrier, the principle of operation of the embodiment shownin FIG. 3 is closely akin to that of the embodiment shown in FIG. 1. Itis the use of clutch means to lock up two members of the planetary gearset which provides the direct drive mode, and the locking of the sun orthe ring gear which provides the gear reduced mode.

Referring to the embodiment shown in FIG. 4, a ring gear held overdriveconfiguration is set out. The components for the overdrive transmissionshown in FIG. 4 are the same as for the underdrive embodiment of FIG. 3with the input and output members being reversed. Thus, the output ofthe transmission shown in FIG. 4 is the shaft 312 and the input isprovided through the planet gear carrier 332 by its attachment to theengine drive by means of an annular member 314.

A planetary gear set is provided, comprising a sun gear 322 affixed tothe output shaft 312, a plurality of planet gears 324 positioned aboutthe sun gear 322, and a ring gear 326 about the planet gears 324. Theplanet gears 324 are supported by a planet carrier 332 having a pin 336,needle bearing 338 and thrust washers 339 for each planet gear 324. Theplanet carrier 332 is provided with an integrally formed cylindricalportion 346 being supported about the shaft 312 by means of a one wayclutch 348 and bearings 349. The integrally formed bearing portions 349of the clutch 348 provides axial and radial support for the planet gearcarrier 332 about the shaft 312. The one way clutch 348 serves to dampthe torsional effects of the engine by preventing counterrotation of theshaft 312.

The cylindrical portion 346 of the carrier 332 is splined to allow axialmovement of a cone clutch 350 along it under the opposing influences ofa spring 352 and a thrust bearing 355. The thrust bearing 355 ispreferably controlled by an annular hydraulic actuator 357.

The ring gear 326 is supported about the shaft 312 by a bearing 363which allows the shaft 312 to rotate relative the ring gear 326. A firstcover member 365 is supported relative to the ring gear 326 by a one wayclutch 370 and bearings 371. The clutch 370 allows the ring gear 326 torotate in the direction of engine rotation only, and the bearing portion371 of the clutch 370 provides axial and radial support for the covermember 365 about the ring gear 326.

In this embodiment, the output is the shaft 312, and a pulley 375 isaffixed thereto. A second cover member 377 is sealingly joined to thefirst cover member 365 such as by bolts 378 and an O-ring 379, and issupported about the input cylindrical portion 346 by a bearing 380.

This ring gear held drive unit has a direct drive mode of operationwherein the output pulley 375 rotates at the speed of the input planetgear carrier 332, and a high gear mode of operation wherein the pulley375 rotates at a speed greater than that of the input shaft 312.

The direct drive mode is provided by engaging the cone clutch 350 andthe ring gear 326 by causing the thrust bearing 355 to slide the clutch350 axially along the cylindrical portion 346 of the planet gear carrier332. In this regard, the cone clutch 350 is provided with a frictionalworking surface 383 which is engageable with a compatible outer surface384 of the ring gear 326. Engagement of the cone clutch 350 and the ringgear 326 causes the locking together of the ring gear 326 and planetgear carrier 332 thereby causing the planet gear system to rotate as aunit.

At the desired switching speed, the actuator 357 releases the thrustbearing 355 allowing the cone clutch 350 to disengage the ring gear 326under the influence of the spring 352. The ring gear 326 is preventedfrom counterrotation by means of the one way clutch 370 and is thus,held stationary. The planet gear system is then able to provide astepped up gear ratio from the gear carrier 332 input to the outputshaft 312.

As explained above with respect to the embodiment shown in FIG. 2, thisring gear held overdrive transmission will provide an overdrive gearratio at lower engine speeds and switch to the gear reduced direct drivemode at higher engine speeds. The switching point will depend on avariety of factors which will be apparent to the skilled person.

The description of the preferred embodiments of the invention has beenmade with reference to the automobile application. However, it should beunderstood that the invention is not so limited and has application to avariety of situations where accessories or the like are driven by anengine.

I claim:
 1. An underdrive accessory transmission associated with anengine, comprising:a planetary gear set comprising a sun gear having anintegrally formed shaft, a plurality of planet gears positioned aboutand drivingly engaging the sun gear, a planet gear carrier, and a ringgear positioned about and drivingly engaging the planet gears, whereinsaid ring gear provides rotational input to the transmission from theengine; a fixed cover for the transmission; cone clutch slidably affixedon the shaft of the sun gear and being capable of axial movement alongthe shaft, the clutch having frustoconical working surfaces engageablewith compatible surfaces of either the ring gear or the cover; means forsliding the cone clutch axially along the shaft of the sun gear; anoutput shaft, the planet gear carrier being affixed about the outputshaft; and a one way clutch and support bearing being positioned betweenthe sun gear and the output shaft, the clutch allowing the output shaftto rotate only in the direction of engine rotation, wherein the coneclutch provides a direct drive from the engine to the output shaft whenit is engaged with the ring gear, the cone clutch provides a neutralmode of operation when it is disengaged from both the ring gear and thetransmission cover, and the cone clutch provides an underdrive to theoutput shaft when it is engaged with the cover.
 2. A transmission asclaimed in claim 1, wherein the cover comprises a first portionsupported about the output shaft by a bearing, and a second portionaffixed to the first portion and being supported about the ring gear bya bearing.
 3. A transmission as claimed in claim 1, wherein the meansfor sliding the cone clutch comprise a spring positioned between the sungear and cone clutch for biasing the clutch toward engagement with thecover, and an actuator having a thrust bearing positioned in oppositionto said spring, the thrust bearing being capable of sliding the clutchinto firm engagement with the ring gear in opposition to the springforce.
 4. A transmission as claimed in claim 3, wherein the actuator ishydraulic.
 5. A transmission as claimed in claim 3, wherein the actuatoris electromechanical.
 6. A transmission as claimed in claim 1, whereinthe ring gear is supported about the output shaft by a bearing.
 7. Atransmission as claimed in claim 1, further comprising thrust washerspositioned at each end of each planet gear to restrict the axialmovement thereof.
 8. An underdrive accessory transmission associatedwith an engine, comprising:a planetary gear set comprising a sun gearhaving an integrally formed shaft, a plurality of planet gearspositioned about and drivingly engaging the sun gear, a planet gearcarrier, and a ring gear positioned about and drivingly engaging theplanet gears, wherein said ring gear provides rotational input to thetransmission from the engine; a fixed cover for the transmission; a coneclutch slidably affixed on the shaft of the sun gear and being capableof axial movement along the shaft, the clutch having frustoconicalworking surfaces engageable with compatible surfaces of either the ringgear or the cover; means for sliding the cone clutch axially along theshaft of the sun gear; an output shaft, the planet gear carrier beingaffixed about the output shaft, and the sun gear being supported by abearing about the output shaft; and a one way clutch and supportbearings being positioned between the ring gear and the output shaft,the clutch allowing the output shaft to rotate only in the direction ofengine rotation, wherein the cone clutch provides a direct drive fromthe engine to the output shaft when it is engaged with the ring gear,the cone clutch provides a neutral mode of operation when it isdisengaged from both the ring gear and the transmission cover, and thecone clutch provides an underdrive to the output shaft when it isengaged with the cover.
 9. A transmission as claimed in claim 8, whereinthe cover comprises a first portion supported about the output shaft bya bearing, and a second portion affixed to the first portion and beingsupported about the ring gear by a bearing.
 10. A transmission asclaimed in claim 8, wherein the means for sliding the cone clutchcomprise a spring positioned between the sun gear and cone clutch forbiasing the clutch toward engagement with the cover, and an actuatorhaving a thrust bearing positioned in opposition to said spring, thethrust bearing being capable of sliding the clutch into firm engagementwith the ring gear in opposition to the spring force.
 11. A transmissionas claimed in claim 8, further comprising thrust washers positioned ateach end of each planet gear to restrict the axial movement thereof. 12.A transmission as claimed in claim 10, wherein the actuator ishydraulic.
 13. A transmission as claimed in claim 10, wherein theactuator is electromechanical.